Mehmet Akbaba

An active battery cell balancing topology without using external energy storage elements

Cell balancing circuits are important to extent life-cycle of batteries and to extract maximum power from the batteries. A lot of power electronics topology has been tried for cell balancing in the battery packages. Active cell balancing topologies transfer energy from the cells showing higher performance to the cells showing lower performance to balance voltages across the cells of the battery using energy storage elements like combination of inductor-capacitor or transformer-capacitor or switched capacitor or switched inductor. In this study an active balancing topology without using any energy storage element is proposed. The idea is similar to the switched capacitor topology in which a capacitor or capacitor banks is switched across the cells of battery to balance the voltages. Since a basic battery cell model includes capacitance because of capacitive effect of the cell, this capacitive effect can be utilized in cell balancing. Hence the equalizer capacitors in switched capacitor topology can be eliminated and the cells of battery can be switched with each other. This allows faster energy transfer and hence results in quick equalization. The proposed topology removes the need of extra energy storage elements like capacitors which frequently fails in power electronic circuits, reduces the losses inserted by extra energy storage elements and cost and volume of the circuits and simplifies control algorithm. The proposed balancing circuit can be implemented according to the application requirement. The proposed topology is simulated in MATLAB/Simulink environment and showed better results in terms of balancing speed in comparison to switched capacitor topologies.

A novel PV sub-module-level power-balancing topology for maximum power point tracking under partial shading and mismatch conditions

Partial shading and mismatch conditions among the series-connected modules/sub-modules suffer from a nonconvex power curve with multiple local maxima and decreased peak power for the whole string. Energy transfer between the sub-modules brings them to the same operating voltage, and this collective operation produces a convex power curve, which results in increased peak power for the string. The proposed topology benefits from the switched-capacitor (SC) converter concept and is an application for sub-module-level power balancing with some novelties, including stopping the switching in absence of shading, string-level extension, and a reduced number of power electronics components as compared to those in the literature. Reduction in the number of power electronics components is realized by the fact that two sub-modules share one SC converter. This leads to reduced power electronics losses as well as less cost and volume of the converter circuit. Insertion loss analysis of the topology is presented. The proposed topology is simulated in the PSpice environment, and a prototype is built for experimental verification. Both simulation and experimental results confirm the loss analysis. This proves that with the proposed topology it is possible to extract almost all the power available on the partially shaded string and transfer it to the load side.

Implementation of differential power processing concept to switched-capacitor topology for PV sub-module level power balancing

Non-convex power characteristic curve with decreased peak power and with multiple local maxima occurs because of the partial shading and mismatching conditions among the series connected modules/sub-modules/cells. A number of power electronics topology has been proposed to equalize voltage of each series connected sub-module while providing an extra current path circuitry for mismatch current. The equalization is done by energy transfer between the sub-modules which brings all sub-modules to the same operating voltage and this collective operation produces a convex output power curve with increased peak power. A power electronics solution including minimum number of components and having higher efficiency is essential in this type of application from the perspective of installation costs and overall efficiency. This paper realizes a differential power processing (DPP) version of the recently presented sub-module level power balancing topology which uses nearly half of the converter number in comparison to the related literature. The DPP version of the topology provides improvement in efficiency for matched conditions and for some arbitrary partial shading patterns conditions over the string. PSpice simulation results are provided to show advantage of the approach in comparison to single output version.

A simple-novel indirect algorithm for tracking maximum power under rapid or slow irradiation and temperature changes

A novel indirect method for maximum power point tracking is proposed in this study. The proposed method, utilizing the linear relationship between the solar irradiation and the maximum power point current, directly provides the maximum power point current and hence the maximum power points trajectory. Therefore it does not require utilization of any search algorithm. Also it has been investigated that the maximum power point current is almost independent of the solar module temperature. Due to this interesting behavior, the proposed method has also superior response for the solar modules working under large temperature ranges. Therefore it has significant advantage over the conventional indirect methods using short circuit current or open circuit voltage. The proposed method is implemented on a boost type converter in MATLAB simulation environment and showed better results in terms of stability and power harvested from the solar module. The method is suitable for the solar systems such as used with micro-inverters.